1. Field of the Invention
The invention relates to electrode active material that can inhibit an irreversible reaction which reduces an irreversible capacity, thus enabling a high capacity to be maintained even when used at a high potential.
2. Description of the Related Art
A lithium-ion secondary battery is a classic example of a secondary battery that charges and discharges by cations such as lithium ions traveling between electrodes. Material that can absorb and release lithium ions can be used for the electrode active material of such a secondary battery. One example of such a material is carbonaceous material such as graphite which is an example of negative electrode active material. On the other hand, an example of positive electrode active material is an oxide which has lithium and a transition metal as constituent elements, such as lithium nickel oxide or lithium cobalt oxide (hereinafter, such an oxide may also be referred to as a “lithium-containing composite oxide”). Moreover, in recent years, chemical compounds having an olivine structure, e.g., chemical compounds represented by the general expression LiMPO4 (M=Mn, Fe, Co, Cu, V), are promising materials for positive electrode active material due in part to their large theoretical capacity.
Meanwhile, Japanese Patent Application Publication No. 2005-158673 (JP-A-2005-158673) describes electrode active material which mainly consists of an amorphous metal-phosphate complex that includes an olivine structure. With the electrode active material that mainly consists of the metal-phosphate complex, an amorphous body can be synthesized from an inexpensive metal oxide at an extremely low cost and in a short period of time by rapid cooling compared with a crystalline body of related art. What is more, the resultant amorphous body seems to display the same battery properties as the crystalline body.
However, when an amorphous metal-phosphate complex is used at a high potential, as it is when used in a vehicle, a side reaction with the electrolyte solution causes an irreversible reaction which results in irreversible capacity, and as a result, sufficient charging and discharging was unable to be performed.